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Hurricane Sandy - Model and Medium Range Discussion


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RPM is the Rapid Precision Model from WSI. It's a 4km model based off the WRF-ARW. To my own surprise it has been fairly accurate 48 hrs out from landfall. It nailed Isaac's timing and landfall 48 hours out even catching the little jog and stall it had after landfall (all in the 48 hr fct). Tim Heller has a POP blog about it for tropical storm Beryl. The RPM always seems to have a windshield wiper effect with each run when systems are too far out to sea but really zones in on landfall and becomes more consistent run to run within 48 hours of landfall. Research has shown that the better the definition of the initial vortex the WRF-ARW has the more the error in hurricane track and intensity forecast decreases. I assume this is why the RPM seems so useless less than 48 hours out unless the storm is hugging a coast where more sampling of the air is taking place thus more data to better define the vortex. Having said that and from experience watching the RPM's performance with tropical systems I believe Sandy is too far OTS as of right now to put much faith the RPM.

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I'm gonna go out on a limb and say it's coorect with the windspeeds and wrong on the central pressure. Hurricane IKe was like 990MB when it produced 65kt windspeeds in Pittsburgh!! Gotta love downsloping.

If this storm stalls, I bet the strongest winds will be in the downslope areas east of the mountains. A little bit of rain cooled air can even aid with the sinking motion hence windspeeds in those areas.

Better analog Hazel was up to 970MB when it produced the famous 100mph gust at Battery.

slp20.png

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Trending towards the EURO

Yup and more importantly (at least in my opinion) is that the Euro has been consistently on the southern edge of the track envelope. Although my gut tells me that the latest small shifts in the Euro will be corrected by a slight northward trend. If I had to put money on it, I would say a NJ "landfall" ... which would be bad news for many with the magnitude of the CAD and the lower level geopotential height gradient expected.

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This is going to be way worse than Irene.

That all depends if its 10 miles North of NYC or 10 miles south of NYC. I'd hate to be a media forecaster if models are showing it right over the city 24hrs out. Error on the side of caution,. but you also have to practice dodging rocks, because they might try to stone you to death if you forecast a 20ft storm surge and there's nothing.

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00z RGEM looking ominous with 48h position 31N 75W under 556 dm upper low ... 12h trend is NNE to that point (3N 1E) ... eyeballing the likely path from 48h to 96h will predict GGEM takes monster low N then NNW to New Jersey landfall. Just a guess from previous runs and trends, 940 mbs will be on the 84h e ACY. RGEM of course is now done.

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Is any model or ensemble member showing rapid acceleration? In the back of my mind is the suspicion that this is like a 5% risk, especially seeing that solutions are once again diverging rather than converging. Rapid acceleration without much intensification would be a fairly benign solution, but with a pressure drop below 955, another form of high impact with the bad timing aspect added.

Please note before I get flamed again, 5% risk disclaimer. By rapid acceleration I would be implying Long Island landfall before mid-day Monday.

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The high and low tide measurements for NY Harbor and vicinity for Monday and Tuesday will be comparable, though slightly less than what was present for Irene. During Irene, I believe an annual maximum tide was present. I don't know if Monday afternoon's high tide or Tuesday's morning's high tide will be more impacting in this case.

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Are we looking at an even more southern solution now?

The NHC has the track more to the south pretty much into Delaware. When the storm actually turns NW towards the east coast will be determined with the phasing with the upper level disturbance. Depending on when this happens should ultimately dictate the landfall area. A phase that occurs sooner will result in a southern landfall. It is very important to note that the size of this storm will cause the impacts to be felt far from the center so the exact landfall location should not be the primary concern.

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